For years, fluorescent lamps have been commonly known and widespread lighting modules as efficient alternatives for incandescent light bulbs. However, with the advent of LED lamp, even more efficient and long-lived lighting means are available. Therefore, there is a demand for replacing existing fluorescent lamps with LED lamps.
Currently available fluorescent lamps are usually operated with an electrical ballast (also called electronic control gear, ECG) for regulating and limiting the current that is provided to the fluorescent lamp and for providing an ignition voltage during a startup process of the fluorescent lamp. The electrical ballast is part of the lamp fixture for the fluorescent lamp.
Replacing existing electrical ballasts in existing lamp fixtures would be labor-intensive and thus requires substantial expenses. Therefore, operating LED lamps with already installed electrical ballasts is favorable. In order to provide an LED lamp that is compatible with the electrical ballast, currently available LED lamps comprise electronic drivers for adapting the voltage and/or current provided by the ballast to the requirements of the lighting module of the LED lamp, which comprises the light-emitting diodes. Otherwise, electronic and/or optoelectronic components of the LED lamp might be damaged or destroyed by the ballast due to high voltages that are produced during the starting sequence. Further, since the power consumption of an LED lamp is lower than that of a fluorescent lamp, without the electronic driver, the electrical ballast would operate in an unstable status.
However, currently available electronic drivers have some disadvantages. For example, during the preheating stage, flickering of the LED lamp might occur due to an unstable input current provided by the electrical ballast. Further, after ignition, flickering of the LED lamp could occur, in particular in the case of the LED lamp being dimmed with a dimmer. In general, the flickering may be due to a combination of a low output power and the ripple current provided by the electrical ballast.
One solution to these problems would be to increase the power consumption of the LED lamp. Thereby, the operating voltage of the LED lamp would be larger than the input voltage provided by the electrical ballast during the preheating stage. This would, however, require increasing the number of light-emitting diodes in the LED lamp and would thus be expensive. A further solution would be to detect the high ignition voltage and to connect the lighting module of the LED lamp to the electrical ballast only after ignition has been finished. Though, this approach could result in an overcurrent at the lighting module after ignition. For reducing the flickering, a linear circuit for filtering the ripple current provided by the electrical ballast could be added to the electronic driver, but this would lead to a high power consumption of the LED lamp due to losses in the linear circuit.